It has become common practice to cut thin sheets of aluminum into various patterns with the use of a routing machine. Such machines were formerly limited to working on softer materials, such as wood, plastics, and other synthetics. Advances in metallurgy now make it possible for routing bits to be able to engage the softer metals for extended periods of time without losing their cutting edges. This technique has become widely used in the manufacture of signs, where large panels have to be cut out into predetermined patterns according to custom specifications. Large computer-controlled routing machines are easily capable of handling panels 4'.times.8', and larger. Once the desired pattern of cutout areas has been introduced into the computer control, the machine proceeds to complete the job automatically.
Where the router isolates a particular area on the work sheet to produce an "island", the rotation of the router bit has a tendency to bite into the material that is almost fully isolated, and flip it out of position. This usually also results in a distortion of the adjacent metal areas. It has been common practice to mount the aluminum work sheets on a backing panel of some relatively inexpensive material, and to attempt to secure the aluminum to the backing material with enough security that the isolated areas of the sheet metal are held with sufficient firmness for the router to continue its operations as these particular areas are isolated. The presence of the backing panel, incidentally, also tends to minimize the formation of a cutting burr on the underside of the work sheet.
Attempts have been made to secure the aluminum work sheet to the backing panel with some form of adhesive effect, and double-coated adhesive tape has been used for this purpose. Essentially, such tape has a plastic base, with adhesive on both sides. One side is stuck to the backing panel, and the other is prepared to receive the aluminum work sheet. It should be noted that this arrangement slightly elevates the aluminum work sheet out of engagement with the backing panel in the areas where the tape has been applied. This is undesirable. Another problem has been the result of the engagement of the router bit rotating at high speed as it goes through a taped area. The heat generated by the cutting action tends to melt the plastic material of the tape, and to gum up the router bit to the point where the cutting action is interfered with. Very extensive cleanup time is characteristically associated with this type of routing procedure.